Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Aug. 08, 2019	Jun. 29, 2018
Cover page.
Document Type	10-K/A
Document Annual Report	true
Document Period End Date	Dec. 31, 2018
Document Transition Report	false
Entity File Number	001-36050
Entity Registrant Name	BMC Stock Holdings, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-4687975
Entity Address, Address Line One	8020 Arco Corporate Drive, Suite 400
Entity Address, City or Town	Raleigh
Entity Address, State or Province	NC
Entity Address, Postal Zip Code	27617
City Area Code	919
Local Phone Number	431-1000
Title of 12(b) Security	Common stock, par value $0.01 per share
Trading Symbol	BMCH
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 1,390
Entity Common Stock, Shares Outstanding		66,649,109
Entity Central Index Key	0001574815
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	true
Amendment Description	Explanatory Note On February 28, 2019, BMC Stock Holdings, Inc. (“we”, “us” or the “Company”) filed its Annual Report on Form 10-K for the fiscal year ended December 31, 2018 (the “Original 10-K”). On August 8, 2019, subsequent to the issuance of the Original 10-K, management, in consultation with the Audit Committee of our Board of Directors, concluded that there was a material weakness in internal control that existed as of December 31, 2018 and continued through the end of the second quarter of 2019, which resulted in the prior period misstatement explained below. A “material weakness” is a deficiency, or a combination of deficiencies, in internal control over financial reporting, such that there is a reasonable possibility that a material misstatement of annual or interim financial statements would not be prevented or detected on a timely basis. Specifically, management identified that a former credit manager within one of our local operations violated our credit policy by intentionally misapplying certain customer payments, both within a single customer balance as well as across multiple customer balances, and created inappropriate debit memos, all with the intent to manipulate the aging of certain unpaid customer invoices. These inappropriate activities resulted in an understatement of the Company’s provision for doubtful accounts in previously issued annual and interim financial statements (the “Prior Period Misstatement”). The Company has corrected for such Prior Period Misstatement by recording during the three and six months ended June 30, 2019 an out of period bad debt expense of $4.3 million in selling, general and administrative expenses and a corresponding decrease to accounts receivable, net of allowances. The Company has concluded that the financial impact of the Prior Period Misstatement is not material to any of its previously issued financial statements and that the correction of such Prior Period Misstatement is not material to either the three or six months ended June 30, 2019, or to the expected financial results for the year ended December 31, 2019. The Company is filing this Amendment No. 1 to Annual Report on Form 10-K/A (this “Amendment”) solely for the purpose of amending and restating the Original 10-K with respect to: (i) the risk factor related to the maintenance of effective internal control and the remediation of material weaknesses included in Item 1A, (ii) the audited consolidated financial statements included in Item 8 to include the restated report of PricewaterhouseCoopers LLP, the Company’s independent registered public accounting firm, to reflect that the Company did not maintain, in all material respects, effective internal control over financial reporting as of December 31, 2018, based on criteria established in Internal Control - Integrated Framework (2013) and (iii) the disclosure included in Item 9A. “Controls and Procedures”, in each case to reflect the material weakness. As required by Rule 12b-15 under the Securities Exchange Act of 1934, the Company’s principal executive officer and principal financial officer are providing new currently dated certifications. In addition, the Company is filing a new consent from PricewaterhouseCoopers LLP. Accordingly, this Amendment amends Item 15. “Exhibits, Financial Statement Schedules” in the Original 10-K to reflect the filing of the new certifications and consent. Other than the foregoing, there are no changes being made to the Original 10-K. In addition, except as specifically described above, this Amendment does not reflect events occurring after the filing of the Original 10-K, nor does it modify or update disclosures therein in any way. Among other things, forward-looking statements made in the Original 10-K have not been revised to reflect events that occurred or facts that became known to us after the filing of the Original 10-K, and any such forward looking statements should be read in their historical context.
Current Fiscal Year End Date	--12-31